Epicyclic gear system

ABSTRACT

An epicyclic gear system (A) has a sun gear ( 2 ), a ring gear ( 4 ) located around the sun gear, and planet gears ( 6 ) located between and engaged with sun and ring gears. In addition, it has a carrier ( 8 ) including a carrier flange ( 30 ) offset axial from the planet gears, carrier pins ( 34 ) projecting from the carrier flange into the planet gears, and bearings ( 72 ) between the planet gears and the carrier pins so that the planet gears rotate on the pins. Each bearing includes an inner race ( 46 ) having tapered raceways ( 56 ) presented away from the carrier pin, opposing tapered raceways ( 24 ) on the ring gear, and tapered rollers ( 70 ) organized rows between the raceways. Whereas the carrier pin is cantilevered from the carrier flange, the inner race is cantilevered from the carrier pin remote from the carrier flange, and this insures that the axes (Y) about which the planet gears rotate remain parallel to the central axis (X) of the system.

RELATED APPLICATIONS

This application derives and claims priority from InternationalApplication PCT/US02/20069, filed Jun. 24, 2002, and published underInternational Publication Number WO 03/002891 A1, and is acontinuation-in-part of U.S. non-provisional application Ser. No.09/894,665, filed Jun. 28, 2001, now abandoned.

TECHNICAL FIELD

This invention relates in general to gear systems and, moreparticularly, to an epicyclic gear system.

BACKGROUND ART

The typical epicyclic or planetary gear system basically has a sun gearprovided with external teeth, a ring gear provided with internal teeth,and several planet gears located between the sun and ring gears andhaving external teeth which mesh with the teeth on the sun and ringgears. In addition to its gears, the typical system has a carrier towhich the planet gears are coupled. Either the sun gear, the ring gear,or the carrier is held fast, while power is delivered to and taken fromthe remaining two components, and thus power is transferred through theplanetary system with a change in angular velocity and an inverse changetorque.

The sun and ring gears for all intents and purposes share the same axis,a central axis, while the planet gears revolve about radially offsetaxes that are parallel to the central axis—or at least they should be.Often the offset axes and the central axis are not parallel, and as aconsequence the planet gears skew slightly between sun and ring gears.This causes excessive wear along the teeth of the planet, sun and ringgears, generates friction and heat, and renders the entire system overlynoisy.

The problem certainly exists in straddle carriers. With this type ofcarrier the pins on which the planet gears rotate extend between twocarrier flanges in which the pins are anchored at their ends. Thecarrier experiences torsional wind up which causes one carrier flange torotate slightly ahead of the other flange. Not only does this skew thepin for each of the planet gears such that one end liescircumferentially ahead of the other end, but it also causes the leadingend of the pin to dip toward the central axis and the other end to drawaway from the central axis. The end result is a poor mesh between theplanet gears and the sun and ring gears, and of course the friction,wear and noise associated with poorly meshed gears. To counteract thistendency, some planetary systems rely on gears that are wider thannecessary and thus offer greater tolerance to skewing along the gearcontact. But these systems can occupy excessive space and can be quiteheavy.

Other transmissions rely on a double cantilever arrangement at the pinsfor their planetary gears to maintain the planet gears and the sun andring gears properly meshed. In this arrangement the carrier has a singlecarrier flange located beyond the ends of the planet gears, and thecarrier pins project from that flange into, and indeed through, thegears. Each carrier pin has one end anchored in the carrier flange andits other end anchored in a sleeve which turns back over the pin tosupport the planet gear. U.S. Pat. No. 3,303,713 to R. J. Hicks shows adouble cantilevered arrangement. Often an antifriction bearing is fittedbetween the sleeve and the planet gear. But antifriction bearingsconsume space, making the planet gears excessively large in diameter,which in turn makes the entire gear system too large and heavy.

SUMMARY OF THE INVENTION

The present invention resides in an epicyclic gear system that has a sungear, a ring gear around the sun gear and at least one planet gearlocated between and engaged with the sun and ring gears. A carrierflange is offset axially from the planet gear and a carrier pin projectsfrom it into the planet gear. An inner race is attached to the carrierpin remote from the carrier flange, and it has a raceway which ispresented toward a raceway carried by the planet gear. Rolling elementsare organized in a row between the opposed raceways to enable the planetgear to revolve about the carrier pin. The invention also resides in acarrier and bearing for such a gear system.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is an exploded perspective view of an epicyclic gear systemconstructed in accordance with and embodying the present invention;

FIG. 2 is a sectional view of the gear system at one of its planet gearsand showing the coupling between the planet gear and the carrier; and

FIG. 3 is a sectional view of the gear system similar to the system ofFIG. 2, but showing a modified coupling.

BEST MODE FOR CARRYING OUT THE INVENTION

Referring now to the drawings, a planetary transmission A (FIG. 1),which is actually an epicyclic gear system, has the capacity to transmitpower of considerable magnitude, given its size and weight. In short, ithas a high power density. In contrast to some planetary transmissions,the transmission A relies on meshing gears that are quite narrow, yetthe teeth of those gears remain properly meshed, even when transmittingsubstantial power and torque. The transmission A has a central axis X ofrotation about which torque is transferred to the transmission A anddelivered from it. The transmission A basically includes a sun gear 2having its axis coincident with the central axis X, a ring gear 4 whichsurrounds the sun gear 2 and shares the axis X with it, and planet gears6 which mesh with and rotate between the sun and ring gears 2 and 4about axes Y that are offset radially from, yet parallel to, the centralaxis X. In addition, the transmission A has a carrier 8 to which theplanet gears 6 are coupled, and the carrier 8 likewise shares thecentral axis X.

Referring more specifically to the sun gear 2, it is attached to a shaft12 or some other supporting structure with which it normally rotates,but it may be fixed against rotation in some installations. The sun gear2 has external teeth 14 which are presented outwardly away from the axisX.

The ring gear 4 is typically fixed, and thus does not rotate, althoughit may rotate in some installations. In any event, the ring gear 4 hasinternal teeth 18 which are presented inwardly toward the axis X andtoward the external teeth 14 on the sun gear 2 and lie concentric withthem. The ring gear 4 may be part of or integrated into a housing forthe transmission A.

An annular space exists between the sun and ring gears 2 and 4, and theplanet gears 6 occupy that space. Each has external teeth 22 which meshwith the external teeth 14 or the sun gear 2 and the internal teeth 18on the ring gear 4. Thus, when the sun gear 2 rotates relative to thering gear 4 about the axis X or vice versa, the planet gears 6 willrevolve, each about its offset axis Y that lies parallel to the centralaxis X. The planetary gears 6 are hollow, with each having two raceways24 (FIG. 2) which taper downwardly to an intervening surface 26 locatedmidway between the ends of the gear 6. The large ends of the raceways 24for each planet gear 6 open out of the ends of the gear 6.

The carrier 8 includes (FIG. 1) a carrier flange 30 to which all of theplanet gears 6 are coupled, it being offset axially beyond correspondingends on each of the gears 6. Normally, the carrier 8 rotates about theaxis X, although it may remain fixed in some installations. When thecarrier 8 rotates, it is usually coupled to a shaft 32 that lies alongthe axis X. In addition to the carrier flange 30, the carrier 8 hascarrier pins 34 which project from the flange 30 into the planet gears6, their axes generally corresponding to the axes Y of rotation for theplanet gears 6.

More specifically, the carrier flange 30 opposite each planet gear 6 hasa tapered hole 36 (FIG. 2). The carrier pins 34, on the other hand, havetapered surfaces 38 which lead out to threaded ends 40. The taperedsurfaces 38 conform in configuration to the tapered holes 36 in theflange 30 and indeed fit snugly into the tapered holes 36 so that thepins 34 project from the face of the carrier flange 30 that is presentedtoward the planet gears 6. The threaded ends 40 project beyond the otherface of the carrier flange 30 where they are engaged by nuts 42 whichare turned down snugly against that face. This lodges the carrier pins34 at their tapered surfaces 38 firmly in the carrier flange 30. Thus,each pin 34 is, in effect, cantilevered from the carrier flange 30.

Each carrier pin 34 projects through its planet gear 6, and at theopposite end of the gear 6, that is the end remote from the carrierflange 30, is fitted to an inner race 46 which the planet gear 6 alsoencircles. The inner race 46 has an end wall 48 and a sleeve 50 formedintegral with the end wall 48. Indeed, the sleeve 50 turns backwardlyfrom the end wall 48 into the interior of the gear 6 and thus encirclesthe carrier pin 34. The end wall contains a bore 52 into which the endof the carrier pin 34 fits with an interference fit. At its very end thecarrier pin 34 is joined to the end wall 48 along a weld 54. Thus, theinterference fit together with the weld 54 secure the inner race 46firmly to the carrier pin 34. The interior surface of the sleeve 50 issomewhat larger than the carrier pin 34, and as a consequence the innerrace 46 at its end wall 48 is cantilevered from the remote end of thecarrier pin 34.

The sleeve 50 of the inner race 46 lies within the interior of theplanet gear 6 and has two tapered raceways 56 which taper downwardly toa separating rib 58. The raceways 56, which have their centers along theaxis Y, are presented outwardly away from the axis Y and toward theraceways 24 on the gear 6, each raceway 56 on the inner race 46 beingopposite one of the raceways 24 on the gear 6. On the other hand, theseparating rib 58 lies opposite the intervening surface 26 of the gear6. Each raceway 56 on the inner race 46 tapers in the same direction asthe raceway 24 toward which it is presented on the planet gear 6. Theraceway 56 closest to the carrier flange 30 leads out to a thrust rib 60that is formed integral with the sleeve 50 of the inner race 26. Theother raceway 56 leads out to a cylindrical mounting surface 62 thatsurrounds the end wall 48. The mounting surface 62 has a rib ring 64fitted to it with an interference fit and further secured with a weld 66at its end. The rib ring 64 extends axially from the weld 66 to thelarge end of the tapered raceway 56, so the rib ring 64 forms anotherthrust rib, similar in function to the rib 60 at the end of the innerrace 46 that is remote from the carrier flange 30.

The annular region between each planet gear 6 and inner race 46 that thegear 6 surrounds is occupied by rolling elements in the form of taperedrollers 70 organized into two rows. One row lies along the integralthrust rib 60 that is adjacent to the carrier flange 30 and contacts theopposed raceways 24 and 56 at that end, while the other row lies alongthe rib ring 64 that surrounds the end wall 48 of the inner race 46 andcontacts the raceways 24 and 56 at that end. Indeed, the tapered rollers70, which are formed from a bearing-grade steel, contact the raceways 24and 56 along their tapered side faces, there being generally linecontact here. They also bear against the thrust rib 60 and rib ring 64at their large end faces. The thrust rib 60 and rib ring 64 prevent therollers 70 from moving up the raceways 24 and 56 and being expelled fromthe annular region between the planet gear 6 and the inner race 46. Therollers 70 of each row are on apex, meaning that the conical envelopesin which the side faces of the rollers 70 of a row lie will have theirapices located at a common point along the axis Y. This produces purerolling contact between the side faces of the rollers 70 and theraceways 24 and 56. While the rollers 70 of each row may be separatedwith a cage, preferably they are not so confined. This enables each rowto contain the maximum number of rollers 70.

A cage, of course, will separate the rollers 70 of a row, so that theydo not contact each other. But when the cage is eliminated, adjacentrollers 70 can contact each other along their tapered side faces. Toretard metal adhesion at contacting side faces, the rollers 70 along atleast their tapered side faces should have a tribological coating thatretards adhesion or at least every other roller 70 should have such acoating in it. One suitable coating includes particles of noncrystallinemetal carbide and an amorphous hydrocarbon matrix in which the particlesare embedded. The tribological coating may be applied to the rollers 70by physical vapor deposition, by chemical deposition, or by acombination of the two. U.S. patent application Ser. No. 10/114,832,filed 2 Apr. 2002, for the invention of G. Doll and G. Fox entitled“Full Complement Antifriction Bearing”, which invention is assigned toThe Timken Company, discloses other tribological coatings which willsuffice for the rollers 70 and procedures for applying them. Thatapplication is incorporated herein by reference.

The rollers 70 together with the inner race 46 and the raceways 24 onthe planet gear 6 form a double row tapered roller bearing 72 thatcouples the planet gear 6 to the carrier pin 34 about which the gear 6rotates. Indeed, the bearing 72 has the capacity to facilitate rotationof the planet gear 6 about the axis Y with minimal friction, whileconfining the gear 6 radially and axially on the carrier pin 34. Inother words, the bearing 72 takes thrust loading in both axialdirections. Moreover, the bearing 72 is set to a condition of lightpreload, and as a consequence no axial or radial clearances exist withinit. This enables the gear 6 to rotate on the carrier pin 34 withoutaxial or radial free motion and without wobbling.

The carrier pins 34 possess a measure of flexibly and indeed will flexwell within their elastic limits when torque is transferred through theplanet gears 6. The double cantilever arrangement enables the axes Y toremain parallel to the axis X and hence the planet gears 6 remainproperly meshed with the sun and ring gears 2 and 4. Thus, the planetgears 6, and likewise the sun and ring gears 2 and 4, need not beexcessively wide to account for off-center gear contact.

To assemble the carrier 8, each carrier pin 34 at its cylindrical end isforced into the bore 52 in the carrier flange 48 of the inner race 46for that pin 34. Then the carrier pin 34 at its end is welded to the endwall 48, producing the weld 54. Thereupon, the rollers 70 for the rowremote from the end wall 48 are placed along the raceway 56 that leadsup to the thrust rib 60, with the large end faces of those rollers being70 against the rib 60. Next the planet gear 6 is installed over theinner race 46 and the row of rollers 70 on that race 46. The leadingraceway 24 in the gear 6 seats against the side faces of those taperedrollers 70. This leaves an annular void between the raceways 24 and 56at the opposite end planet gear 6. More rollers 70 are inserted intothis void with their small ends leading, thus creating a second row ofrollers 70 having their large ends located along the end of the mountingsurface 62 for inner race 46. With the gear 6 and the two rows ofrollers 70 in place around the inner race 46, the rib ring 64 is forcedover the mounting surface 62 on the inner race 46, and advanced towardthe large ends of the rollers 70 that are at the mounting surface 62. Asthe rib ring 64 approaches the large end faces of the rollers 70, thegear 6 is rotated to insure that the rollers 70 of the two rows seatagainst the raceways 24 and 56 and along the thrust rib 60 and rib ring64. After the rib ring 64 comes against the large end faces of therollers 70 in the row that is along it, the bearing 72 will enterpreload. The advance continues a short distance until the bearing 72acquires the proper preload. Then the rib ring 64 is welded to the innerrace 46, producing the weld 66. The gear 6, rollers 70, inner race 46and carrier pin 34 constitute a subassembly 76, and enough subassemblies76 are produced in the foregoing manner to complete the carrier 8.

Within each subassembly 76 the tapered surface 38 of the carrier pin 34extends beyond the open end of the sleeve 50 for the inner race 46 andbeyond the corresponding end of the planet gear 6 as well. The taperedsurface 38 of the carrier pin 34 is inserted into one of the taperedholes 36 of the carrier flange 30, whereupon one of the nuts 42 isengaged with the threaded end 40 that projects out of the flange 30. Thenut 42 is turned down firmly against the carrier flange 30 to draw thetapered surface 38 of the carrier pin 34 snugly into the tapered hole36. This secures the carrier pin 34 and inner race 46 firmly to thecarrier flange 30. The remaining subassemblies 76 are installed on thecarrier flange 30 in a like manner.

With the carrier 8 so assembled, it is installed over the sun gear 2 andinto the ring gear 4 such that the external teeth 22 on the planet gears6 engage the external teeth 14 in the sun gear 2 and the internal teeth18 on the ring gear 4.

When torque is applied to the shaft 12 to rotate the sun gear 2, theplanet gears 6 revolve and move along the ring gear 4, thus impartingrotation to the carrier 8 and the shaft 32 extended from it. The angularvelocities of the two shafts 12 and 32 differ and with that difference achange in the torque ensues. Of course, the torque may be applied to theshaft 32 and taken from the shaft 12. Actually, any one of the sun gear2, ring gear 4 and carrier 8 may be held fast and torque delivered toand taken from the remaining two components.

In a modified subassembly 78 (FIG. 3) the carrier pin 34 is formedintegral with the inner race 46.

The cantilever of the carrier pins 34 from the carrier flange 30 and thecantilever of the inner races 46 from the carrier pins 34, that is theso-called “double cantilever”, insures that the axes Y of rotation forthe ring gears 6 remain parallel to the center axis X. As a consequence,the ring gears 6 do not require excessive width to resist skewing. Theinner races 46, being mounted directly on the carrier pins 34, insteadof on intervening components, together with the integration of the outerraceways 24 into the planet gears 6, enables the bearings 72 to be of adiameter that is smaller than the diameters of bearings in moreconventional epicyclic gear systems. This, in turn, can permit use ofsmaller sun and ring gears 2 and 4, and otherwise render the entiretransmission highly compact and light in weight.

In lieu of a double row tapered roller bearing 70, each planet gear 6may be coupled to its carrier pin 34 on the carrier 8 with a double rowangular contact ball bearing or even with a cylindrical or sphericalroller bearing. Also, more or less than four planet gears 6 may be usedbetween the sun gear 2 and ring gear 4.

1. An epicyclic gear system having a central axis and comprising: a sungear located along the central axis; a ring gear located around the sungear and also along the central axis; planet gears located between andengaged with the sun and ring gears for rotation about offset axes thatare spaced from the central axis; each planet gear carrying first andsecond outer raceways which taper downwardly toward each other so thatthey have their least diameters where they are closest; and a carriercoupled with the planet gears, the carrier including a flange and pinsprojecting from the flange into the planet gears, there being a separatepin for each planet gear, each pin at one of its ends being cantileveredfrom the carrier flange, the carrier also including an inner race oneach pin with the inner race being cantilevered from its pin remote fromthe flange and including a sleeve that extends into the planet gear forthe pin where it is spaced from the pin, the sleeve having first andsecond inner raceways which are presented toward and taper in the samedirection as the first and second outer raceways, respectively, thesleeve also having a thrust rib projecting beyond the large end of thefirst inner raceway and a mounting surface at the large end of thesecond inner raceway, the inner race also including an initiallyseparate rib ring located against the mounting surface of the sleevesuch that the rib ring projects beyond the large end of the secondraceway for the inner race; first tapered rollers arranged in a rowbetween the first raceway for each planet gear and inner race, withtheir large ends being against the thrust rib; and second taperedrollers arranged in a second row between the second raceways for eachplanet gear and inner race and having their large ends against the ribring.
 2. A gear system according to claim 1 wherein each inner race alsoincludes an end wall to which the sleeve for that inner race isattached, and the inner race is cantilevered from its pin at the endwall.
 3. A gear system according to claim 2 wherein the sleeve and endwall for each inner race are formed integral.
 4. A gear system accordingto claim 2 wherein the pin and the end wall for the inner race on thatpin are formed integral.
 5. A gear system according to claim 1 whereinthe thrust rib for each inner race is formed integral with the sleevefor that inner race.
 6. A gear system according to claim 5 wherein thethrust rib for each inner race is located closer to the carrier flangethan the rib ring for that inner race.
 7. A gear system according toclaim 6 wherein the second raceway for each inner race is located inpart around the location at which that inner race is cantilevered fromits pin.
 8. A gear system according to claim 1 wherein the mountingsurface is cylindrical and the rib ring fits around the mountingsurface.
 9. A gear system according to claim 8 wherein the mountingsurface and rib ring surround the location at which the inner race iscantilevered from the pin.
 10. A gear system according to claim 1wherein the rollers of each row are capable of contacting each other;and wherein at least some of the rollers in each row are covered with atribological coating capable of retarding metal adhesion.
 11. Anepicyclic gear system having a central axis; said gear systemcomprising: a sun gear located along the central axis; a ring gearlocated around the sun gear and also along the central axis; planetgears located between and engaged with the sun and ring gears forrotation about offset axes that are spaced from the central axis, eachplanet gear carrying an outer raceway that is presented inwardly towardits offset axis; a carrier coupled with the planet gears and including aflange and pins projecting from the flange into the planet gears, therebeing a separate pin for each planet gear, each pin at one of its endsbeing cantilevered from the carrier flange, the carrier also includingan inner race located between each planet gear and the pin whichprojects into that planet gear and having an inner raceway which ispresented outwardly toward the outer raceway carried by the planet gear,the inner race being cantilevered from its pin remote from the flange,but otherwise being spaced from the pin, with the location where theinner race is cantilevered from the pin being surrounded in part by theinner raceway; and rolling elements arranged in a row between the outerand inner raceways for each planet gear and inner race and also beinglocated in part around the location where the inner race is cantileveredfrom the pin.
 12. A gear system according to claim 11 wherein the row ofthe rolling elements between each planet gear and inner race is one oftwo rows, with one row being closer to the flange than the other row;and wherein only a portion of said other row surrounds the location atwhich the inner race is cantilevered from the pin.
 13. A gear systemaccording to claim 11 wherein the rolling elements of each row arecapable of contacting each other; and wherein at least some of therolling elements of each row are covered with a tribological coatingcapable of retarding metal adhesion.
 14. An epicyclic gear system havinga central axis and comprising: a sun gear located along the centralaxis; a ring gear located around the sun gear and also along the centralaxis; planet gears located between and engaged with the sun and ringgears for rotation about offset axes that are spaced from the centralaxis; a carrier flange located beyond the planet gears; carrier pinsprojecting from the carrier flange into the planet gears, there being aseparate pin for each planet gear, with each pin being cantilevered fromthe carrier flange; and a bearing between each pin and the planet gearinto which the pin projects, each bearing including: first and secondouter raceways on the planet gear where they are inclined oppositelywith respect to the offset axis for the planet gear and presentedinwardly toward the axis; an inner race located within the planet gearand around the pin, the inner race being attached to the pin remote fromthe flange and projecting toward the flange from the location of theattachment of the inner race to the pin, beyond which the inner race isspaced from the pin, whereby the inner race is cantilevered from thepin, the inner race having first and second inner raceways which areinclined with respect to the offset axes, with the first inner racewaybeing inclined in the same direction as the first outer raceway and thesecond inner raceway being inclined in the same direction as the secondouter raceway, whereby the first and second inner raceways are inclinedoppositely, first rolling elements arranged in a row between the firstouter and inner raceways and second rolling elements arranged in a rowbetween the second outer and inner raceways, the bearing being in acondition of preload so that no clearances exist between the rollingelements and the raceways.
 15. A gear system according to claim 14wherein the raceways are tapered and the rolling elements are taperedrollers.
 16. A gear system according to claim 15 wherein the outerraceways taper downwardly toward each other so that they are closest attheir least diameters, wherein the inner raceways taper downwardlytoward each other so that they are closest at their least diameters, andthe tapered rollers of the first row have their large ends presentedaway from the tapered rollers of the second row and vice versa.
 17. Agear system according to claim 16 wherein the inner race includes asleeve which is spaced from the pin, and the first and second innerraceways are on the sleeve; wherein the sleeve has a thrust rib thatprojects outwardly beyond the large end of its first inner raceway;wherein the inner race also includes an initially separate rib ring thatis attached to the sleeve and projects beyond the large end of thesecond inner raceway; wherein the large ends of the tapered rollers inthe first row are against the thrust rib and the large ends of thetapered rollers in the second row are against the rib ring.
 18. A gearsystem according to claim 17 wherein the sleeve of the inner race has amounting surface that extends axially beyond the large end of the secondinner race at a diameter not exceeding the diameter of that large end,and the rib ring fits around the mounting surface.
 19. A gear systemaccording to claim 14 wherein the rolling elements of each row arecapable of contacting each other; and wherein at least some of therolling elements are covered with a tribological coating capable ofretarding metal adhesion.